L2: Acid, Bases, Buffers (Biological) Flashcards
How does the body attempt to compensate for different types of acid-base imbalances?
Respiratory acidosis: disturbance = high pCO2, compensation = increase bicarb conc. Respiratory alkalosis: disturbance = low pCO2, compensation = decrease bicarb conc. Metabolic acidosis: disturbance = low bicarb conc, compensation = decrease pCO2 Metabolic alkalosis: disturbance = high bicarb conc, compensation = increase pCO2
How do the lungs and kidneys act together to maintain acid-base balance?
The lungs can either take in additional CO2 to reduce pH or can expel CO2 to increase pH. The kidneys can keep or expel bicarbonate to manipulate pH levels as well.
What are some common causes of metabolic alkalosis?
Acute alkali administration, vomiting, gastric aspiration, diuretics
What are some common causes of respiratory alkalosis?
Anxiety, pain, high altitude, mechanical hyperventilation
Which biological buffers predominate in the blood and cytoplasms of cells? At what ranges?
The phosphate buffer system predominates in the cytoplasm of cells. Ranges from 6.9 to 7.4 depending on cell type. Muscle = ~7.06. The bicarbonate/CO2 buffer system predominates in the blood of the body. Ranges from ~7.35 to 7.45.
How does one determine the value of pKa to predict what form(s) a weak acid will predominate at, at a given pH?
The value of the pKa can help determine which forms of the acid will be dominant at a certain pH. When the pH=pKa the concentrations of acid and base are equal. When pHpKa the base form dominates.
Why is the bicarb buffer system considered an ‘open system’?
The bicarbonate system is “open” because both CO2 and bicarbonate can be manipulated separately by the lungs and kidneys, respectively.
What types of acid-base imbalances are caused by changes in level of CO2?
Respiratory acidosis is caused by higher levels of CO2 resulting in a decrease in blood pH. Respiratory alkalosis is caused by lower levels of CO2 resulting in an increase in blood pH.
Define buffer. What is the Henderson-Hasselbach equation? Explain this equation in terms of the bicarbonate buffer system seen in the blood.
A buffer is a solution of weak acid and conjugate base which does not completely dissociate in water. The buffer will help maintain a solution within a certain pH range, generally close to the pKa of the acid contained in the buffer. The Henderson-Hasselbalch equation can be used to determine the pH of a solution when the pKa and concentrations of both acid and base are known. It is shown as pH = pKa + log [A-]/[HA]. The biological form of this equation for the blood: pH = 6.10 + log [HCO3-]/[CO2 dissolved]. The pKa of the bicarb buffer has been experimental determined based on physiological conditions. The bicarb:CO2 dissolved concentrations is therefore what determines the blood’s pH. Altering these via lungs/kidneys, alters the pH.
Explain what is meant by a mixed acid-base imbalance? Give an example.
Patient’s who have an acidosis and alkalosis. For example, a pt with chronic lung disease who is also on diuretics could have respiratory acidosis and metabolic alkalosis.
What are the methods to maintain pH in the body? Which is quickest, slowest?
Chemical buffering (instantaneous) > regulation of CO2 via lungs (3-4 hours) > blood HCO3- and H+ by kidneys (3-5 days)
What are the effects of hypo- and hyperventilation on blood pH?
Hypoventilation increases the partial pressure of CO2 and will result in a decrease of blood pH. Hyperventilation decreases the partial pressure of CO2 and will result in an increase of blood pH.
Provide example calculations to show your understanding of how a patient’s pH is calculated after given quantities of H+ ions are added or removed. (normal bicarb conc = 24 mmol/L, normal co2 dissolved conc = 1.2 mmol/L or 40 torr)
2 moles H+ ions added: pH = 6.10 + log [24 - 2]/[1.2] = 7.36 *note bicarb is decreasing by 2, although H+ ions are added 2 moles H+ ions removed: pH = 6.10 + log [24 + 2]/[1.2] = 7.43 *note bicarb is increasing by 2, although H+ ions are removed
What types of acid-base imbalances are caused by changes in the level of HCO3-?
Metabolic acidosis is caused by lower levels of HCO3- resulting in a decrease in blood pH. Metabolic alkalosis is caused by higher levels of HCO3- resulting in an increase in blood pH.
What is the definition of pH? How does direction of pH change as concentration of H+ ions change?
pH is a measure of the acidity or basicity of a solution. The pH decreases as the concentration of hydrogen ions increase, and increases as the concentration of hydrogen ions decreases.
